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GAS EXCHANGE in “Animals”

GAS EXCHANGE in “Animals”. Cells require O 2 for aerobic respiration and expel CO 2 as a waste product. Fick’s Law of Diffusion. Gas exchange involves the diffusion of gases across a membrane Rate of diffusion (R) is governed by Fick’s Law: R = DA p d

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GAS EXCHANGE in “Animals”

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  1. GAS EXCHANGE in “Animals” • Cells require O2 for aerobic respiration and expel CO2 as a waste product

  2. Fick’s Law of Diffusion • Gas exchange involves the diffusion of gases across a membrane • Rate of diffusion (R) is governed by Fick’s Law: • R = DA p d D= diffusion constant (size of molecule, membrane permeability, etc) A= area over which diffusion occurs p = pressure difference between sides of the membrane d = distance across which diffusion must occur

  3. Fick’s Law of Diffusion R = DA p d To maximize diffusion, R can be increased by: Increasing A (area over which diffusion occurs) Increasing p (pressure difference between sides of the membrane) Decreasing d (distance across which diffusion must occur) Evolutionary changes have occurred to maximize R

  4. Figure 42.18 The role of gas exchange in bioenergetics

  5. GAS EXCHANGE in “Animals” • The part of the organism across which gases are exchanged with the environment is the respiratory surface

  6. Respiratory Surfaces • Must be moist • plasma membranes must be surrounded by water to be stable • Must be sufficiently large • maximize A in Fick’s Law

  7. Comparative Respiratory Systems • Cell Membranes • in unicellular organisms • some simpler animals (sponges, cnidarians, flatworms)

  8. Comparative Respiratory Systems • Respiratory surface = a single layer of epithelial cells • separates outer respiratory medium (air or water) from the organism’s transport system (blood)

  9. Comparative Respiratory Systems • Skin (cutaneous respiration) • Skin must be moist • organisms with flat or wormlike bodies so skin in sufficient surface area • or in frogs and some turtles to supplement respiration using lungs

  10. Comparative Respiratory Systems • Specialized region of body is folded and branched to provide large surface area • This maximizes A in Fick’s Law • Also decrease d by bringing the respiratory medium close to the internal fluid • Three such systems: • Gills (Aquatic organisms) • Trachea (insects) • Lungs (terrestrial vertebrates)

  11. Figure 42.19 Diversity in the structure of gills, external body surfaces functioning in gas exchange

  12. Gills • most aquatic organisms • outfoldings of the body surface specialized for gas exchange • Water is the respiratory medium

  13. Water as Respiratory Medium • Respiratory surface always moist • Oxygen content of water is much less than that of air • denser medium so harder to ventilate

  14. Ventilation • Any method that increases the flow of the respiratory medium across the respiratory surface • This maximizes p in Fick’s Law • By constantly have new air or new water with more oxygen

  15. Ventilation • requires a lot of energy to ventilate gills b/c water is denser than air • pumping operculum, ram ventilation

  16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Buccal cavity Operculum Oral valve Water Mouth closed, operculum opened Opercular cavity Gills Mouth opened, jaw lowered Gills

  17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gills Operculum Water flow Gill arch Water flow Gill raker Gill filaments Oxygen- rich blood Oxygen- deficient blood Oxygen- rich blood Oxygen- deficient blood Water flow Gill filament Lamellae with capillary networks Blood flow

  18. Countercurrent Exchange • Enhances gas exchange in the gills of fish • blood is continually loaded with O2 b/c it meets water with increasing O2 concentration • Increases p in Fick’s Law

  19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Countercurrent Exchange Concurrent Exchange Water (100% O2 saturation) Water (50% O2 saturation) Blood (85% O2 saturation) Blood (50% O2 saturation) 85% 100% 80% 90% No further net diffusion 70% 80% 60% 70% 50% 60% 50% 50% 40% 50% 40% 60% 30% 70% 30% 40% 20% 80% 20% 30% 10% 90% 10% 15% Blood (0% O2 saturation) Blood (0% O2 saturation) Water (15% O2 saturation) Water (100% O2 saturation) a. b.

  20. Air as respiratory medium • Higher oxygen concentration • ventilation is easier b/c air is less dense • respiratory surface loses water to air by evaporation

  21. Air as respiratory medium • Solution… • fold respiratory surface inside the body

  22. Trachea • Air tubes that branch throughout the body • finest tubes (tracheoles) extend to nearly every cell in the body • gas diffuses across moist epithelium that lines the terminal ends

  23. Figure 42.22 Tracheal systems

  24. Trachea • Found in insects • Open Circulatory system of insects is NOT involved in transporting gases • Ventilation • diffusion • body movements

  25. Lungs • Localized in one area of body • circulatory system must transport gases

  26. Lungs • Ventilation • Positive pressure breathing - frogs

  27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nostrils open Air External nostril Buccal cavity Esophagus Lungs a. Nostrils closed Air b.

  28. Lungs • Ventilation • Negative pressure breathing- mammals

  29. Negative pressure breathing

  30. Negative pressure breathing Inspiration Sternocleido- mastoid muscles contract (for forced inspiration) Air Lungs Muscles contract Diaphragm contracts a. Expiration Air Muscles relax Abdominal muscles contract (for forced expiration) Diaphragm relaxes b.

  31. Blood flow Bronchiole Smooth muscle Nasal cavity Nostril Pharynx Glottis Larynx Pulmonary venule Trachea Left lung Right lung Pulmonary arteriole Left bronchus Alveolar sac Capillary network on surface of alveoli Diaphragm Alveoli Lungs

  32. Lungs • Ventilation • air sacs act as bellows in birds • air flows in one direction during both inhalation & exhalation

  33. Cycle 1 Inspiration Expiration Parabronchi of lung Anterior air sacs Posterior air sacs Lung Trachea Trachea Anterior air sacs Posterior air sacs Cycle 2 Inspiration Expiration a. b. Lungs of Birds

  34. Transport of Gases • Occurs in the circulatory system when needed

  35. Transport of Gases • O2 is transported by respiratory pigments • hemoglobin on red blood cells or hemocyanin in the plasma

  36. Transport of Gases • CO2 is transported by respiratory pigments and dissolved in the plasma and in red blood cells as bicarbonate ion (HCO3-)

  37. Gas Exchange in Plants • Stomata • tiny pores on the underside of leaves • lead to air spaces in the mesophyll

  38. Gas Exchange in Plants • Guard cells • regulate the opening & closing of stomata • turgid - stomata open, flaccid - stomata close

  39. Figure 36.12x Stomata on the underside of a leaf

  40. Figure 36.12 An open (left) and closed (right) stoma of a spider plant (Chlorophytum colosum) leaf

  41. Figure 36.13a The mechanism of stomatal opening and closing

  42. Figure 36.13b The mechanism of stomatal opening and closing

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